1. Field of the Invention
The present invention relates to a method for injecting mixed refrigerant (in the following description, the mixed refrigerant is defined as a mixture of at least two or more kinds of refrigerants, and for example, it is commonly named R-410A, R-407C or the like. It is hereinafter merely referred to as "refrigerant") into a refrigerant circuit comprising at least a compressor, a condenser, an expansion device and an evaporator which are connected to one another through a refrigerant pipe while keeping the refrigerant to be injected in a liquid state, and more particularly to a method for injecting a liquid refrigerant while preventing the refrigerant from being compressed under the liquid state (hereinafter referred to as "compression under liquid") in a compressor.
2. Description of Related Art
There has been known a refrigerating machine such as a separation type air conditioner, a show-case or prefabricated type refrigerator (freezer) or the like in which various elements constituting a refrigerant circuit are installed while these elements are shared to and disposed in an indoor unit and an outdoor unit respectively. When the indoor unit and the outdoor unit of such a refrigerating machine are connected to each other to make the refrigerant circuit works effectively, the length of a pile through which the indoor and outdoor units are connected varies in accordance with the set-up places of these units. If the indoor or outdoor unit is set up in such a place as to increase the length of the refrigerant pipe, the amount of refrigerant which is beforehand filled in the refrigerant circuit (in a heat exchanger of the outdoor unit) before the indoor and outdoor units are set up would become insufficient. Therefore, the fill amount of the refrigerant is required to be varied in accordance with the length of the pipe.
Further, in various refrigerating machines containing not only the above type refrigerating machine, but also a private type room air conditioner, which need a pipe connection work for connecting the indoor and outdoor units at a set-up place, there may be occur the case where the refrigerant filled and sealed in the refrigerant circuit may gradually leak from the refrigerant circuit due to failure of the pipe connection work or the like in the progress of the operation of the refrigerating machine after set up. In this case, the injection (supplement) of the refrigerant into the refrigerant circuit is needed to prevent reduction in refrigerating capacity (power).
When refrigerant is filled (injected) into a refrigerant circuit, particularly when single refrigerant is injected into a refrigerant circuit, a desired amount of refrigerant is generally sucked under a gaseous state from a service port of the refrigerant circuit (in general, from the position which is at the upstream side of the compressor and at a low pressure position in the refrigerant circuit) by the negative pressure which is produced through the operation of the compressor while measuring the weight of a refrigerant filling (injecting) bomb, and then the refrigerant filling (injecting) work is finished when the weight of the bomb is reduced by a desired fill (injection) amount.
Recently, substitute refrigerant (HFC mixed refrigerant) such as R-407C, R-410A or the like has been frequently used to prevent the environmental destruction of the ozone layer by CFCs (Chlorofluorocarbons). However, it has been impossible to inject the mixed refrigerant into the refrigerant circuit while keeping the mixed refrigerant under a gaseous state. For example, R-407C is non-azeotropic mixed refrigerant having the following composition: HFC32:HFC125:HFC134=23 wt %:25 wt %:52 wt %, and the composition of R-407C varies when it is vaporized. Therefore, when the non-azeotropic mixed refrigerant is injected into the refrigerant circuit, it is required to inject the mixed refrigerant into the refrigerant while keeping the mixed refrigerant under a liquid state.
In general, the service port of the refrigerant circuit is formed at the refrigerant suck-in side of the compressor. Therefore, when the liquid refrigerant whose amount exceeds the liquid refrigerant capacity of an accumulator is injected from the service port into the refrigerant circuit, the liquid refrigerant is directly sucked into the compressor, and the refrigerant is compressed under the liquid state (i.e., the liquid-compression occurs) in the compressor, resulting in failure of the compressor. Here, the liquid refrigerant capacity of the accumulator is defined as the permissible maximum refrigerant amount which can be stocked in the accumulator so that the liquid refrigerant moves from the accumulator to the compressor (i.e., no liquid-compression occurs in the compressor).
In the case of a relatively compact type refrigerating machine (refrigerator or the like) having no accumulator, the liquid-compression problem as described above would occur if liquid refrigerant is injected so that the injection amount thereof exceeds the natural vaporization amount thereof in a refrigerant pile of the refrigerant circuit.